I have purchased a 1989 Invader 240 rear cabin. When I open the engine hatch, I see two white plastic tanks, on on the left beside the batteries and one on the right right at the transom. I think the one on the right is for fresh water. The one on the left has two hoses connected to the side of the tank about 2/3 of way down the side. I have no idea what this is for. Also the boat used to have a marine toilet, where would the holding tank be? If anyone can give me some idea as to what the tanks are used for, I would greatly appreciate it.